Flash client won't stop auto-filling username/password

I'm trying to get the client to NOT remember my username/password, clearly unchecking box to remember password. But every time I launch the client it gets filled in regardless of what I do. I've tried:

clearing all cookies for bridgebase.com

clearing history

deleting local storage/Flash local storage

changing password (old password still gets auto-filled)

login with another alias (old username/password still gets auto-filled)

Microsoft Edge browser seems to behave correctly.
Help??

Edit: progress, but only sort of:looks like the flash control panel accessed by right-clicking in firefox on the flash app doesn't really do anything anymore. To really clear flash local storage have to go to windows control panel (old fashioned one), find flash control panel app, clear from there. At that point my username/password are now cleared. But now can't get them to save with "remember password". It's like Firefox (unlike Edge, which seems to store to a different location, under #AppContainer?) doesn't seem to save new data at all, but was able to read old data.
Oh well, I guess flash is going away. But the HTML 5 version doesn't seem to have a "remember password" checkbox? I'd like that option.

So you've done something that's blocking Flash local storage for the bridgebase.com domain. You should be able to go into the Flash control panel and remove this block.

I've definitely not done anything overtly to block Flash. The control panel is set to allow all sites storage by default and always has been, www.bridgebase.com was allowed and had data (until I force cleared it to clear my username/password). There was no reason for me to ever go in and block storage for bridgebase domain or any other domain. Microsoft edge browser still saves the data fine, albeit to %appdata%\roaming\macromedia\flash player\#sharedobjects\[random string]\#appcontainer\www.bridgebase.com; whereas I think firefox wants it to be under ...\[random string]\www.bridgebase.com rather than under #appcontainer but now doesn't write any of the .sol files. Previously obviously it worked as my username/password and settings were saved from some earlier software combo.
It's more likely some past few months forced software update whether firefox/flash/windows that broke something?

Ran some experiments, cleared bridgebase, set flash to "prompt if new site asks to save data". When I launched the bridgebase client I immediately got the prompt, which I allowed. The container folder for the data was created, but no files created (under firefox; edge still works but in the different location).

Hmm after deep dive on google, I seem to have found a solution.
Problem appears to have been introduced in Firefox 64, version 63 unaffected.
Solution for now:
go to about:config, use search to find "sandbox"
change dom.ipc.plugins.sandbox-level.flash to 2, restart firefox.